Conventionally, most analysis of tiny amount of molecules relating to clinical diagnosis, food hygiene, and environmental analysis has been carried by processing a sample with an apparatus such as a centrifugal separator, a gas chromatography apparatus, and a liquid chromatography apparatus, and then analyzing to a high level of accuracy using a mass spectrometer. These apparatuses are expensive and require specialized knowledge to operate. Therefore, the such separation, measurement, and analysis have been performed by a clinical testing laboratories or an analysis institute. Recently, there is a trend for the need to perform simple and fast diagnosis, analysis and/or measurements at a patient's bedside, and locations where food is processed and imported. More specifically, for example, performing disease diagnosis and analysis of toxic substances in rivers and waste products on site, such as at the patient's bedside, a river, or waste treatment plant, is gaining attention. Consequently, emphasis is being placed on the development of methods and devices capable of separating, measuring, and analyzing a sample simply, rapidly, cheaply, and accurately, yet with a high degree of sensitivity.
In particular, in clinical diagnosis, for early diagnosis of a sickness condition, an important problem to resolve is how to perform detection simply, rapidly, cheaply, and accurately, yet with a high degree of sensitivity, using a small amount of a specimen, while shortening the analysis time and reducing the amount of the specimen (sample) required for the analysis.
Accordingly, recently, to resolve this subject, new devices are being developed which can perform analysis by applying micro fabrication technology. In such devices, fine channels are formed and arranged in a chip several cm in size (square), a very small amount of a specimen (sample) such as blood from a test subject is injected into the chip, and analysis is carried out. Such a device needs functions for collecting blood cells from blood and removing the blood cells, as well as a function for separating a specific component from a small amount of a (living) sample. Various techniques have been developed for such purposes.
For example, a technique is known for separating a specific component by rotating a chip to apply centrifugal force.
JP 3803078 discloses a technique in which blood cells are separated from blood by rotating a chip having fine channels arranged in an approximately horizontal plane, and after stopping rotation, a plasma component is isolated using an external suction pump.
The chip disclosed in JP 3803078 has a structure including (1) a tank for holding blood which includes a blood cell component, (2) a channel which is connected to and positioned further toward the outer circumferential side of the tank holding the blood and which has a function for holding plasma, and (3) a blood cell fraction containing portion which is connected to and positioned on the outer circumferential side of the channel holding plasma.
Furthermore, JP 2006-200923 describes a chemical analysis device capable of isolating serum utilizing centrifugal force, capillarity, and a siphon effect by repeatedly rotating and stopping a chip having fine channels which are arranged in an approximately horizontal plane.
This chip has (1) a tank for holding a suspension such as blood including a blood cell component, (2) a tank for holding a separation liquid such as serum which is further on the outer circumferential side than the tank holding the suspension, and (3) a tank for holding an insoluble component such as blood cells, the tank being connected to the separation liquid holding tank by a narrow portion such as a weir, this tank being further toward the outer circumferential side than the tank holding the separation liquid. In this chip, the tank holding the suspension and the tank holding the separation liquid are connected by a narrow portion such as a weir.
Furthermore, a capillary tube is used for causing capillary flow from the tank holding the separation liquid due to surface tension.
In the chip disclosed in JP 3803078, after blood cell separation, the plasma component is recovered by connecting an external connection suction pump. Therefore, the chip disclosed in JP 3803078 needs an external connection suction pump to be prepared and requires time and efforts for the connection. Thus, this chip cannot be said to be simple, fast, and low-cost analysis means.
The chip disclosed in JP 3803078 has a blood cell fraction containing portion further toward the outer circumferential side than the channel having a function for holding plasma. In this chip, during the isolation and recovery of plasma by a suction pump, the blood cell component needs to adhere to the blood cell fraction containing portion. However, clinical blood specimens exhibit a varied nature in which blood cell characteristics such as viscosity, composition, and hemolysis differ according to individual differences, clinical condition and the like. Therefore, for such a clinical blood specimen, because the adherence of the blood cell component at the blood cell fraction containing portion may be insufficient, the blood cell component may be mixed with and enter the plasma due to the suction force which is applied on the blood cell fraction containing portion during suction recovery with the pump. Thus, to prevent the risk of the blood cell component mixed with and entering the plasma by reducing the suction force applied on the blood cell fraction during suction recovery with a pump, JP 3803078 discloses a technique which employs a narrow structure as the connecting portion of the channel having a function for holding plasma with the blood cell fraction containing portion.
However, since the connecting portion with the channel having a function for holding plasma is a narrow structure, the blood cell fraction containing portion suffers from the problem that the connecting portion tends to become blocked by the blood cell component. Furthermore, since the blood cell fraction containing portion is a sealed space other than the connecting portion with the channel having a function for holding plasma, there is no place for gases to escape. Therefore, for clinical blood specimens having a varied nature in which viscosity, composition and the like differ according to individual differences, clinical condition and the like, a gas layer forms in the blood cell fraction containing portion, which may prevent blood from entering and cause gas bubbles to remain in the blood cell fraction containing portion.
The chip disclosed in JP 2006-200923 does not require an external connection pump, but rather leads serum to a downstream mixing portion due to capillary flow by stopping the chip after a serum separation operation. However, in the chip disclosed in JP 2006-200923, the channel and various tanks are arranged so that the suspension passes through a separation liquid holding tank due to centrifugal force by rotation, then flows through a narrow portion and into an insoluble component holding tank.
More specifically, since the insoluble component holding tank is a sealed space other than a suspension flow inlet, there is no place for gases to escape. Therefore, for clinical blood specimens having a varied nature in which viscosity, composition and the like differ according to individual differences, clinical condition and the like, a gas layer forms in the insoluble component holding tank. This gas layer may prevent the suspension from entering, cause gas bubbles to remain in the insoluble component holding tank, and cause the insoluble component to remain in the separation liquid holding tank. If gas bubbles remain in the insoluble component holding tank, the quantitative performance of the separation liquid may be harmed. In such a case, although providing a vent hole in the insoluble component holding tank improves on this problem, it is impossible to completely prevent gas bubbles from remaining.
Furthermore, the chip disclosed in JP 2006-200923 recovers and isolates serum by a siphon effect produced by causing a separation liquid separated by rotation to capillary flow in a serum capillary tube serving as a separation liquid discharge channel due to surface tension after rotation is stopped, and then again rotating. Thus, it is necessary to cause capillary flow just by surface tension in a fine channel in a state where there is no action of centrifugal force. However, as described above, it is difficult to produce a constantly stable capillary flow for clinical blood specimens such as serum having a varied nature in which viscosity, composition and the like differ according to individual differences, clinical condition and the like. To produce a stable capillary flow, the diameter of the tube needs to be as small as possible. However, decreasing the diameter of the tube increases the risk of the siphon effect easily failing to work due to the entry of solid matter such as blood clots into the serum capillary tube, and the occurrence and entry of gas bubbles inside the capillary tube.
Thus, if a separation liquid such as serum cannot be stably recovered and isolated in a correct amount, an error or a mistake may be produced in the obtained analysis and test result. Especially in the medical field, this is a serious problem.
Moreover, the chip disclosed in JP 2006-200923 has to be rotated, stopped, and again rotated to recover and isolate the serum.
Further, in the case of providing a folded back portion in an overflow channel to increase the quantitative performance, when suspension which has passed the folded back portion during rotation flows toward an overflow liquid holding tank, the suspension which should flow into the insoluble component holding tank may flow back toward the folded back portion due to siphoning. More specifically, pre-separation suspension may flow out due to the occurrence of siphoning caused by suspension which has filled the overflow channel during rotation. Consequently, the quantitative performance may be harmed.
In view of such a situation, it could be helpful to provide a separation chip capable of stably separating an insoluble component and a liquid component in a suspension more accurately without requiring an external device such as an external connection pump. Furthermore, it could also be helpful to provide a method for separating a desired component using this separation chip.